According to a previously proposed standard for a high picture-quality video signal, a field frequency is 60 Hz, a line frequency is 33.75 kHz, and the number of lines per one frame is 1125.
When a television broadcasting of NTSC system is generally broadcasted at present and recording and editing processings and so on are carried out, a field frequency of 59.94 Hz and a line frequency of 15.75 Hz are used and the number of lines per one frame is 525.
While a demand for recording and reproducing a high-resolution video signal and carrying out the broadcasting with using it has been increased, the current system (i.e., the NTSC system or a PAL system) is still dominant in view of a systematic environment. As a result, it is necessary to convert a source recorded by a high-resolution video system into that of the NTSC system for broadcasting, recording and reproducing it. Therefore, it is sometimes observed that a video tape recorder for recording, reproducing and editing the high-resolution video signal is employed in the systematic environment of the NTSC system. Under such circumstance, it is necessary for the video tape recorder of the high-resolution video system to process even a video signal having a field frequency of 59.94 Hz without any problems.
In this case, a recording format used when a signal is recorded on a magnetic tape is a problem. Specifically, if the signals have different field frequencies and are to be recorded on a magnetic tape as they are, two kinds of track formats, i.e., two kinds of track patterns are required.
For example, when a signal is recorded on a magnetic tape with field frequencies of 60 Hz and 59.94 Hz by a digital video tape recorder employing the same recording clock frequency, total lengths of tracks on the magnetic tape becomes 125.275 mm and 125.150 mm, respectively. A difference between the two track lengths is 0.125 mm.
It is not preferable that one video tape recorder employs two kinds of formats, in view of management of a magnetic tape and complication of a hardware.
Therefore, in order to solve the above problem, a recording format is set completely the same by allowing field frequencies (59.94 Hz/60 Hz) to be changed in one video tape recorder in order to reproduce data recorded with a field frequency of 59.94 Hz and vice versa. However, in order to set the tape recording pattern completely the same, crystals for frequency oscillators respectively corresponding to the field frequencies of 59.94 Hz/60 Hz must be prepared, which leads to a problem of the manufacturing costs.